Dielectric ceramic for microwave applications

ABSTRACT

A dielectric ceramic for microwave applications is comprised of: 
     
         X BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 
    
      O 3 ) W1  (Nd 2  O 3 ) W2  } 
     where X, Y, Z lie in the ranges: 11.0≦X≦22.0; 60.0≦Y≦75.0; and 6.0≦Z≦28.0 (X+Y+Z=100) expressed in mole %, and 0&lt;W 1  ≦0.35; 0&lt;W 2  &lt;1; and 0&lt;(1-W 1  -W 2 )&lt;1; where W 1 , W 2  and (1-W 1  -W 2 ) are mole ratios. MnO 2  or Al 2  O 3  may also be added. 
     Alternatively, a dielectric ceramic may comprise: 
     
         X BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 
    
      O 3 ) W1  (Nd 2  O 3 ) W2  }.V Bi 2  O 3   
     where X, Y, Z and V lie in the ranges: 11.5≦X≦21.0; 60.0≦Y≦76.0; 6.5≦Z≦26.0; and 0.1≦V≦5.0 (X+Y+Z+V=100), expressed in mole %, and 0&lt;W 1  &lt;1; 0&lt;W 2  &lt;1; 0≦(1-W 1  -W 2 )&lt;1, where W 1 , W 2  and (1-W 1  -W 2 ) are mole ratios. MnO 2 , CeO 2 , PbO, or Al 2  O 3  may also be added. 
     The dielectric ceramic of the invention has a high dielectric constant ε r  and a high unloaded Q (Q u ), and moreover, the temperature coefficient τ f  of the resonant frequency can be varied over a wide range by varying the composition.

FIELD OF THE INVENTION

This invention concerns a dielectric ceramic for microwave applications,and in particular, a dielectric ceramic composition for microwaveapplications having a high dielectric constant ε _(r), a high unloadedQ, and temperature coefficient τ _(f) which can be made to vary above orbelow zero by varying the composition.

BACKGROUND OF THE INVENTION

It is known that in general, for dielectric resonators for microwavecircuits or temperature compensation ceramic (porcelain) capacitors orthe like, dielectric ceramic (porcelain) compositions are required tohave a high dielectric constant ε _(r) and unloaded Q (Q_(u) =1/tanδ),and it must be possible to design them with any desired value for thetemperature coefficient τ _(f) of the resonant frequency above or belowzero, i.e., with a positive or negative temperature coefficient.Conventionally, such compositions included Bao.TiO₂ systems, MgTiO₃.CaOsystems, ZrO₂.SnO₂.TiO₂ systems, and BaO.TiO₂.Sm₂ O₃.La₂ O₃ systems (seefor example Japanese Patent Kokoku Publication No. 61-14606).

When dielectric resonators or capacitors were manufactured with thesecompositions, however, their dielectric constant ε _(r) was 60 to 80when their temperature coefficient τ _(f) was in the region of 0(ppm/°C.), and this value of dielectric constant was too small to permitthe resonator to be made compact.

SUMMARY OF THE INVENTION

This invention was conceived to overcome the above problems. Anobjective of the invention is therefore to provide a dielectric ceramicfor microwave applications with high dielectric constant ε _(r) andunloaded Q even when the temperature coefficient is in the region of 0(ppm/°C.).

According to one aspect of the invention, a dielectric ceramic formicrowave applications is comprised of barium oxide (BaO), titaniumdioxide (TiO₂), samarium oxide (Sm₂ O₃), lanthanum oxide (La₂ O₃) andneodymium oxide (Nd₂ O₃) represented by the formula:

    X BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }

where X, Y, Z lie in the ranges:

    11.0≦X≦22.0

    60.0≦Y≦75.0

    6.0≦Z≦28.0

    X+Y+Z=100

expressed in mole %, and

    0<W.sub.1 ≦0.35

    0<W.sub.2 <1

    0<(1-W.sub.1 -W.sub.2)<1

where W₁, W₂ and (1-W₁ -W₂) are mole ratios.

In addition to BaO, TiO₂, Sm₂ O₃, La₂ O₃, and Nd₂ O₃, which are the mainconstituents, the dielectric ceramic may also contain MnO₂ as asupplementary constituent to the extent of no more than 3 wt %.

In addition to BaO, TiO₂, Sm₂ O₃, La₂ O₃, and Nd₂ O₃, which are the mainconstituents, the dielectric ceramic may also contain Al₂ O₃ as asupplementary constituent to the extent of no more than 3 wt %.

According to another aspect of the invention, a dielectric ceramic formicrowave applications is comprised of barium oxide (BaO), titaniumdioxide (TiO₂), samarium oxide (Sm₂ O₃), lanthanum oxide (La₂ O₃),neodymium oxide (Nd₂ O₃) and bismuth oxide (Bi₂ O₃), represented by theformula:

    X BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }.V Bi.sub.2 O.sub.3

where X, Y, Z and V lie in the ranges:

    11.5≦X≦21.0

    60.0≦Y≦76.0

    6.5≦Z≦26.0

    0.1≦V≦5.0

    X+Y+Z+V=100

expressed in mole %, and

    0<W.sub.1 <1

    0<W.sub.2 <1

    0<(1-W.sub.1 -W.sub.2)<1,

where W₁, W₂ and (1-W₁ -W₂) are mole ratios.

In addition to the above described main constituents, the dielectricceramic may also contain MnO₂ as a supplementary constituent, to theextent of no more than 2 wt %.

In addition to the above described main constituents, the dielectricceramic may also contain cerium oxide (CeO₂), as a supplementaryconstituent, to the extent of no more than 5 wt %, this amountcorresponding to 0.0606 mole per mole of the main constituents.

In addition to the above described main constituents, the dielectricceramic may also contain lead oxide (PbO), as a supplementaryconstituent, to the extent of no more than 5 wt %, this corresponding to0.0463 mole per mole of the main constituents.

In addition to the above described main constituents, the dielectricceramic may also contain aluminum oxide (Al₂ O₃), as a supplementaryconstituent, to the extent of no more than 3 wt %, this corresponding to0.0609 mole per mole of the main constituents.

In this invention, the constituents of the dielectric ceramic formicrowave applications are specified within the above limits, as aresult, as will be clear from the following experimental results, thedielectric constant ε _(r) and unloaded Q are high even if saidtemperature coefficient τ _(f) is in the region of 0 (ppm/°C.), and thetemperature coefficient τ _(f) can also be given any desired value aboveor below 0, i.e., positive or negative, by varying the composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

We shall now described this invention in more detail with reference tospecific examples.

In the following description, Tables B1, B2, C1, A1, A2, D1, D2 and D3that form the last part of the specification will be referred to. TheseTables shows the results of the experiments or measurements on theexamples according to the invention, and comparative examples.

In the attached Tables, sample numbers marked with the symbols "*" arecomparative samples which are outside the scope of the invention, andother samples are examples according to the invention. Also, in theTables, as well as in the following description, "wt %" denotepercentage in weight.

EXAMPLE B

BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃, Nd₂ O₃ and MnCO₃ of high purity were takenas starting materials, and mixed in the proportions shown in theattached Table B1 and Table B2. This mixture was calcined in air at1060° C. for 2 hours. The calcined material was pulverized in a pot millwith pure water, dewatered and dried to obtain a powder. To the powderwas added a binder to obtain a granule, which was then classified bypassing through a 32 mesh sieve. The granule obtained was molded by adie at a pressure of 1 to 3 ton/cm² to form a circular plate of diameter16 mm and thickness 9 mm. This molded product was then placed in a highpurity alumina case and fired at a suitable temperature in the range1250° C. to 1500° C. for 2 hours so as to obtain a dielectric ceramicmaterial.

The dielectric constant ε _(r) and Q_(u) of the material were measuredby the Hakki-Coleman method. Further, the temperature coefficient τ _(f)of the resonant frequency was found by equation (1) below from theresonant frequencies at the temperatures -40° C. and +85° C., and theresonant frequency at the temperature 20° C. taken as a reference, andthe experimental results were shown in Tables B1 and B2 attached. Theresonant frequency in these measurements was 3 to 4 GHz. ##EQU1## where:f (20° C.)=resonant frequency at 20° C.

f (85° C.)=resonant frequency at 85° C.

f (-40° C.)=resonant frequency at -40° C.

Δ T=measured temperature difference. In this case, Δ T=85-(-40)=125° C.

According to the results of Table B1, if the amount of BaO in thecomposition is less than 11.0 mole % or greater than 22.0 mole %, oralternatively if the amount of TiO₂ is less than 60.0 mole % or greaterthan 75.0 mole %, the unloaded Q (Q_(u)) becomes small and thetemperature coefficient τ _(f) increases, which is undesirable. Further,if the total amount Z of rare earth oxides (Sm₂ O₃, La₂ O₃, Nd₂ O₃) isless than 6.0 mole % or greater than 28.0 mole %, the dielectricconstant ε _(r) and unloaded Q (Q_(u)) again become small and thetemperature coefficient τ _(f) increases, which is undesirable. Further,if the mole ratio W₁ (La₂ O₃) exceeds 0.35, the temperature coefficientτ _(f) is too large which is undesirable. Further, if the mole ratio W₂(Nd₂ O₃) or (1-W₁ -W₂) (Sm₂ O₃) is zero, the temperature coefficient τ_(f) is either too negative or too positive, which is undesirable.

From the above results, therefore, it was found that if the compositionof the main constituents is represented by:

    X BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }

where

    11.0≦X≦22.0

    60.0≦Y≦75.0

    6.0≦Z≦28.0

    X+Y+Z=100

where the mole ratios are specified respectively by:

    0<W.sub.1 ≦0.35

    0<W.sub.2 <1

    0<(1-W.sub.1 -W.sub.2)<1

the composition is suitable for a dielectric ceramic for microwaveapplications.

Table B2 shows the results of measurements carried out on dielectricceramics comprised of BaO, TiO₂, Sm₂ O₃, La₂ O₃ and Nd₂ O₃ as mainconstituents with the further addition of MnO₂, together with theresults for comparative examples. By increasing the amount of MnO₂, theunloaded Q (Q_(u)) can be increased and the temperature coefficient τ_(f) of the resonant frequency can be controlled.

If the amount of MnO₂ exceeds 3 wt %, however, the unloaded Q (Q_(u))decreases and the temperature coefficient τ _(f) increases which isundesirable.

EXAMPLE C

BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃, Nd₂ O₃ and Al₂ O₃ of high purity were takenas starting materials, weighed out in the compositional proportionsshown in the attached Table C1 (In Table C1, and other tables, the marks_(") signify "same as above"), and mixed with pure water in a pot mill.In this Example, the main constituents, i.e. BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃and Nd₂ O₃, were mixed in two different proportions, and the amount ofAl₂ O₃ added as a supplementary constituent was varied.

This mixture was calcined in air at 1060° C. for 2 hours. The calcinedmaterial was processed in the same manner as in Example B to obtain themolded circular plate. The molded product was then placed in a highpurity alumina case and fired at a suitable temperature in the range1250° C. to 1400° C. so as to obtain a dielectric ceramic.

The dielectric constant ε _(r) and unloaded Q (Q_(u)) of the materialwere measured in the same manner as in the Embodiment B, and thetemperature coefficient τ _(f) of the resonant frequency was found byequation (1).

The results of the experiments were shown in the attached Table C1.

According to the experimental results of Table C1, if the amount of Al₂O₃ added to the composition is no greater than 3 wt % with respect tothe main constituents, there is not much change of dielectric constant ε_(r) and unloaded Q (Q_(u)), and in particular, if the amount is 0.2 wt%, unloaded Q (Q_(u)) increases. Further, as the amount of Al₂ O₃ addedincreases, the temperature coefficient τ _(f) varies largely in thenegative direction. If on the other hand the amount of Al₂ O₃ is greaterthan 3 wt %, i.e. in the case of Sample No. 5 and No. 10, the dielectricconstant ε _(r) and unloaded Q (Q_(u)) becomes smaller and thetemperature coefficient τ _(f) becomes highly negative, which isundesirable.

From the above results, therefore, it was found that if the compositionis represented by:

    X BaO.Y TiO.sub.2. Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }

with respect to the main constituents, where:

    11.0≦X≦22.0

    60.0≦Y≦75.0

    6.0≦Z≦28.0

    X+Y+Z=100

expressed in mole %, where the mole ratios are specified respectivelyby:

    O<W.sub.1 ≦0.35

    O<W.sub.2 <1

    O<(1-W.sub.1 -W.sub.2)<1.00

and where Al₂ O₃ is added to the main constituents to the extent of nomore than 3 wt % (excluding 0 wt %), the composition is suitable as adielectric ceramic for microwave applications. The 3 wt % of Al₂ O₃corresponds to 0.0563 mole of Al₂ O₃ per mole of the main constituents,consisting of BaO, TiO₂, Sm₂ O₃, La₂ O₃ and Nd₂ O₃.

EXAMPLE A

BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃, Nd₂ O₃ and Bi₂ O₃ of high purity were takenas starting materials, and mixed with pure water for 20 to 24 hours in apot mill in the proportions shown in the attached Table A1 and Table A2.After dewatering the mixture and drying it, the mixed powder wascalcined in a high purity alumina case at 1060° C. for 2 hours. Thecalcined material was processed in the same manner as in Example B toobtain the molded circular plate. This molded product was then placed ina high purity alumina case and fired at a suitable temperature in therange 1250° C. to 1450° C. for 2 hours so as to obtain a dielectricceramic.

The dielectric constant ε _(r) and unloaded Q (Q_(u)) of the materialwere measured in the same manner as in the Embodiment B, and thetemperature coefficient τ _(f) of the resonant frequency was found byequation (1).

The results of the experiments were shown in the attached Table A1.

According to the results of Table A1, if the amount of BaO in thecomposition is less than 11.5 mole % or greater than 21.0 mole %, oralternatively if the amount of TiO₂ is less than 60.0 mole % or greaterthan 76.0 mole %, the unloaded Q (Q_(u)) becomes small and thetemperature coefficient τ _(f) increases, which is undesirable. Further,if the amount Z of rare earth oxides (Sm₂ O₃, la₂ O₃, Nd₂ O₃) is lessthan 6.5 mole % or greater than 26.0 mole %, the dielectric constant ε_(r) and unloaded Q (Q_(u)) again become small and the temperaturecoefficeint τ _(f) increases, which is undesirable.

Further, as the amount of Bi₂ O₃ increases, dielectric constant ε _(r)and unloaded Q (Q_(u)) improve, but if it exceeds 5 mole %, unloaded Q(Q_(u)) decreases which is undesirable. Further, if the mole ratio W₁(La₂ O₃), W₂ (Nd₂ O₃) or (1-W₁ -W₂) (Sm₂ O₃) are zero, the unloaded Q(Q_(u)) is small or the temperature coefficient τ _(f) is high, which isundesirable.

From the above results, therefore, it was found that if the compositionof the main constituents is represented by:

    X BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }.V Bi.sub.2 O.sub.3

where

    11.5≦X≦21.0

    60.0≦Y≦76.0

    6.5≦Z≦26.0

    0.1≦V≦5.0

    X+Y+Z+V=100

where the mole ratios are specified respectively by:

    0<W.sub.1 <1

    0<W.sub.2 <1

    0<(1-W.sub.1 -W.sub.2)<1

the composition is suitable for a dielectric ceramic for microwaveapplications.

Table A2 shows the results of measurements carried out on dielectricceramics comprised of BaO, TiO₂, Sm₂ O₃, La₂ O₃, Nd₂ O₃ and Bi₂ O₃ asmain constituents with the further addition of MnO₂, together with theresults for Comparative Examples.

By increasing the amount of MnO₂, the unloaded Q (Q_(u)) can beincreased and the temperature coefficient τ _(f) of the resonantfrequency can be controlled. The sinterability of this dielectricceramic composition also improved.

If the amount of MnO₂ exceeds 2 wt %, however, the unloaded Q (Q_(u))decreases and the sinterability of the composition also declines, whichis undesirable.

EXAMPLE D1

BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃, Na₂ O₃, Bi₂ O₃, and CeO₂ of high puritywere taken as starting materials, weighted out in the proportions shownin the attached Table D1, and mixed with pure water in a pot mill. Inthis Example, the main constituents, i.e. BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃,Nd₂ O₃ and Bi₂ O₃, were mixed in two different proportions, and theamount of CeO₂ added as a supplementary constituent was varied.

This mixture was calcined in air at 1060° C. for 2 hours. The calcinedmaterial was processed in the same manner as in Example B to obtain themolded circular plate. This molded product was then placed in a highpurity alumina case and fired at a suitable temperature in the range1250° C. to 1400° C. for 2 hours so as to obtain a dielectric ceramic.

The dielectric constant ε _(r) and unloaded Q (Q_(u)) of the materialwere measured in the same manner as in the Embodiment B, and thetemperature coefficient τ _(f) of the resonant frequency was found byequation (1).

The results of the experiments were shown in the attached Table D1.

According to the measurement results of Table D1, as the amount ofcerium oxide (CeO₂) is increased with respect to the main constituents,dielectric constant ε _(r) and unloaded Q (Q_(u)) decrease after passingthrough a maximum, while the temperature coefficient τ _(f) increasesafter passing through a minimum. The dielectric constant ε _(r) exhibitsa maximum of ε _(r) =89.5 when addition of CeO₂ is 0.2 wt %, andunloaded Q (Q_(u)) exhibits a maximum of 2310 when addition of CeO₂ is 3wt %. Subsequently, both dielectric constant ε _(r) and unloaded Q(Q_(u)) decline. It was found that for compositions where the additionof CeO₂ exceeds 5 wt %, i.e. Sample No. 6 and No. 12, dielectricconstant ε _(r) falls to a very low value of approx. 40, which isundesirable.

From the above results, therefore, it was found that if the compositionis represented by:

    X BaO.Y TiO.sub.2. Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd .sub.2 O.sub.3).sub.W2 }.V Bi.sub.2 O.sub.3

with respect to the main constituents, where:

    11.5≦X≦21.0

    60.0≦Y≦76.0

    6.5≦Z≦26.0

    0.1≦V≦5.0

    X+Y+Z+V=100

expressed in mole %, the mole ratios are specified respectively by:

    0<W.sub.1 <1.0

    0<W.sub.2 <1.0

    0<(1-W.sub.1 -W.sub.2)<1.0,

and CeO₂ is also added to the main constituents to the extent of no morethan 5 wt % (excluding 0 wt %), the composition is suitable as adielectric ceramic for microwave applications. This 5 wt % of CeO₂corresponds to 0.0606 mole of CeO₂ per mole of the main constituents.The sinterability of this dielectric ceramic composition was alsoimproved.

EXAMPLE D2

BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃, Nd₂ O₃, Bi₂ O₃, and PbO of high purity weretaken as starting materials, weighed out in the compositionalproportions shown in the attached Table D1, and mixed with pure water ina pot mill. In this Example, the main constituents, i.e. BaCO₃, TiO₂,Sm₂ O₃, La₂ O₃, Nd₂ O₃ and Bi₂ O₃ were mixed in two differentproportions, and the amount of PbO added as a supplementary constituentwas varied.

This mixture was calcined in air at 1060° C. for 2 hours. The calcinedmaterial was processed in the same manner as in Example B to obtain themolded circular plate. This molded product was then placed in a highpurity alumina case and fired at a suitable temperature in the range1250° C. to 1400° C. for 2 hours so as to obtain a dielectric ceramic.

The dielectric constant ε _(r) and unloaded Q (Q_(u)) of the materialwere measured in the same manner as in the Embodiment B, and thetemperature coefficient τ _(f) of the resonant frequency was found byequation (1).

The results of the experiments were shown in the attached Table D2.

According to the measurement results of Table D2, as the amount of leadoxide (PbO) is increased with respect to the main constituents,dielectric constant ε _(r) increases up to 5 wt %, passes through amaximum of ε _(r) =95.2, and then decreases. Unloaded Q (Q_(u)), on theother hand, decreases with increasing addition of PbO, and falls sharplywhen addition exceeds 5 wt %. Further, temperature coefficient τ _(f)exhibits a minimum at an addition of 3 wt %, then it begins to increaseand rises sharply when addition exceeds 5 wt %. As Sample No. 6 and No.12, have an unloaded Q (Q_(u)) no greater than 1000 and a highlypositive temperature coefficient, it is seen that they are undesirable.

From the above results, therefore, it was found that if the compositionis represented by:

    X BaO.Y TiO.sub.2. Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }.V Bi.sub.2 O.sub.3

with respect to the main constituents, where:

    11.5≦X≦21.0

    60.0≦Y≦76.0

    6.5≦Z≦26.0

    0.1≦V≦5.0

    X+Y+Z+V=100

expressed in mole %, the mole ratios are specified respectively by:

    0<W.sub.1 <1.0

    0<W.sub.2 <1.0

    0<(1-W.sub.1 -W.sub.2)<1.0,

and PbO is also added to the main constituents to the extent of no morethan 5 wt % (excluding 0 wt %), the composition is suitable as adielectric ceramic for microwave applications. This 5 wt % of PbOcorresponds to 0.0463 of PbO per mole of the main constituents. Thesinterability of this dielectric ceramic composition was also improved.

EXAMPLE D3

BaCO₃, TiO₂, Sm₂ O₃, La₂ O₃, Nd₂ O₃, Bi₂ O₃ and Al₂ O₃ of high puritywere taken as starting materials, weighed out in the compositionalproportions shown in the attached Table D1, and mixed with pure water ina pot mill. In this Example, the main constituents, i.e. BaCO₃, TiO₂,Sm₂ O₃, La₂ O₃, Nd₂ O₃ and Bi₂ O₃ were mixed in two differentproportions, and the amount of Al₂ O₃ added as a supplementaryconstituent was varied.

This mixture was calcined in air at 1060° C. for 2 hours. The calcinedmaterial was processed in the same manner as in Example B to obtain themolded circular plate. This molded product was then placed in a highpurity alumina case and fired at a suitable temperature in the range1250° C. to 1450° C. for 2 hours so as to obtain a dielectric ceramic.

The dielectric constant ε_(r) and unloaded Q (Q_(u)) of the materialwere measured in the same manner as in the Embodiment B, and thetemperature coefficient τ _(f) of the resonant frequency was found byequation (1).

The results of the experiments were shown in the attached Table D3.

According to the measurement results of Table D3, if the addition ofaluminum oxide (Al₂ O₃) is no greater than 3 wt %, with respect to themain constituents, the dielectric constant ε _(r) becomes slightly less,but it does not decrease very much. Further, if the addition is notgreater than 1 wt %, unloaded Q (Q_(u)) increases. Further, as additionof Al₂ O₃ increases, the temperature coefficient τ _(f) goes highlynegative, and it is thus possible to change the sign of the coefficientfrom positive to negative by adjusting the addition of Al₂ O₃.

If on the other hand the addition of Al₂ O₃ is greater than 3 wt %, i.e.in the case of Sample No. 6 and No. 12, the dielectric constant ε _(r)is no greater than 50, the unloaded Q (Q_(u)) decreases to 1000 or lessand the temperature coefficient τ _(f) goes very highly negative. It isevident that these properties are undesirable.

From the above results, therefore, it was found that if the compositionis represented by:

    X BaO.Y TiO.sub.2. Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }.V Bi.sub.2 O.sub.3

with respect to the main constituents, where:

    11.5≦X≦21.0

    60.0≦Y≦76.0

    6.5≦Z≦26.0

    0.1≦V≦5.0

    X+Y+Z+V=100

expressed in mole %, the mole ratios are specified respectively by:

    0<W.sub.1 <1.0

    0<W.sub.2 <1.0

    0<(1-W.sub.1 -W.sub.2)<1.0,

and Al₂ O₃ is also added to the main constituents to the extent of nomore than 3 wt % (excepting 0 wt %), the composition is suitable as adielectric ceramic for microwave applications. This 3 wt % of Al₂ O₃corresponds to 0.0609 mole of Al₂ O₃ per mole of the main constituents.

It should be understood that this invention is not limited to theExamples given in the Tables, and compositions which have differentamounts of supplementary constituents within the specified range withrespect to other combinations of the main constituents within thespecified range, will give similar results to those of the aboveExamples.

As is clear from the above description of the various embodiments orexamples, in the microwave region, the dielectric constant ε _(r) andunloaded Q (Q_(u)) of the composition of this invention are high, andfurthermore, the temperature coefficient τ _(f) of the resonantfrequency can be varied over a wide range by varying the composition.

The composition can therefore be used as a dielectric ceramic(porcelain) for microwave resonators or for temperature compensationcapacitors, and it has a high industrial value.

                                      TABLE B1                                    __________________________________________________________________________       X    Y    Z                      τ.sub.f                               No.                                                                              (mole %)                                                                           (mole %)                                                                           (mole %)                                                                           1-W.sub.1 --W.sub.2                                                                 W.sub.1                                                                          W.sub.2                                                                          ε.sub.r                                                                  Q.sub.u                                                                          (ppm/°C.)                          __________________________________________________________________________    1* 15.9 68.2 15.9 1     0  0  78.4                                                                             2,510                                                                            -140                                      2* 15.9 68.2 15.9 0.46  0.54                                                                             0  78.1                                                                             1,694                                                                            159                                       3  15.9 68.2 15.9 0.70  0.15                                                                             0.15                                                                             74.2                                                                             2,597                                                                            -19                                       4  15.9 68.2 15.9 0.50  0.15                                                                             0.35                                                                             76.6                                                                             2,844                                                                            21                                        5  15.9 68.2 15.9 0.30  0.15                                                                             0.55                                                                             77.9                                                                             2,902                                                                            37                                        6  15.9 68.2 15.9 0.10  0.15                                                                             0.75                                                                             78.5                                                                             2,698                                                                            82                                        7  15.9 68.2 15.9 0.50  0.35                                                                             0.15                                                                             79.1                                                                             2,464                                                                            75                                        8  15.9 68.2 15.9 0.30  0.35                                                                             0.35                                                                             78.2                                                                             2,363                                                                            99                                        9  15.9 68.2 15.9 0.40  0.05                                                                             0.55                                                                             82.4                                                                             2,348                                                                            14                                        10 15.9 68.2 15.9 0.30  0.05                                                                             0.65                                                                             82.5                                                                             2,357                                                                            37                                        11*                                                                              15.9 68.2 15.9 0.13  0.52                                                                             0.35                                                                             78.3                                                                             1,863                                                                            173                                       12*                                                                              15.9 68.2 15.9 0     0.48                                                                             0.52                                                                             75.1                                                                             1,750                                                                            154                                       13*                                                                              15.9 68.2 15.9 0     0  1  84.1                                                                             2,210                                                                            120                                       14 16.7 66.6 16.7 0.20  0.05                                                                             0.75                                                                             83.1                                                                             2,263                                                                            56                                        15 16.7 66.6 16.7 0.10  0.05                                                                             0.85                                                                             83.3                                                                             2,303                                                                            72                                        16*                                                                              16.7 66.0 16.7 0.03  0  0.97                                                                             79.5                                                                             2,128                                                                            121                                       17 19.0 75.0  6.0 0.5   0.15                                                                             0.35                                                                             72.3                                                                             2,200                                                                            43                                        18*                                                                              25.0 72.5  2.5 0.50  0.35                                                                             0.15                                                                             51.2                                                                             1,218                                                                            106                                       19*                                                                               9.0 71.0 20.0 0.50  0.35                                                                             0.15                                                                             55.7                                                                             1,139                                                                            143                                       20*                                                                              18.0 50.0 32.0 0.50  0.35                                                                             0.15                                                                             54.2                                                                               872                                                                            131                                       21 11.0 61.0 28.0 0.50  0.15                                                                             0.35                                                                             72.3                                                                             1,800                                                                            31                                        22*                                                                              11.0 80.0  9.0 0.50  0.35                                                                             0.15                                                                             59.3                                                                             1,132                                                                            116                                       23 22.0 60.0 18.0 0.24  0.23                                                                             0.53                                                                             58.8                                                                             1,790                                                                            74                                        __________________________________________________________________________

                                      TABLE B2                                    __________________________________________________________________________                                  τ.sub.f                                     No.                                                                              X  Y  Z  W.sub.1                                                                          W.sub.2                                                                           MnO.sub.2                                                                         ε.sub.r                                                                   Q.sub.u                                                                          (ppm/°C.)                                __________________________________________________________________________     1*                                                                              19.2                                                                             67.5                                                                             13.3                                                                             0.25                                                                             0.35                                                                              0   74.5                                                                              1,852                                                                            19                                              2  19.2                                                                             67.5                                                                             13.3                                                                             0.25                                                                             0.35                                                                              0.5 75.1                                                                              2,133                                                                            15                                              3  19.2                                                                             67.5                                                                             13.3                                                                             0.25                                                                             0.35                                                                              1.5 76.6                                                                              2,427                                                                            25                                              4  19.2                                                                             67.5                                                                             13.3                                                                             0.25                                                                             0.35                                                                              3.0 75.0                                                                              2,111                                                                            47                                               5*                                                                              19.2                                                                             67.5                                                                             13.3                                                                             0.25                                                                             0.35                                                                              5.0 74.1                                                                                960                                                                            96                                              __________________________________________________________________________

                                      TABLE C1                                    __________________________________________________________________________                            Al.sub.2 O.sub.3                                                                        τ.sub.f                                 No.                                                                              X  Y  Z  1-W.sub.1 --W.sub.2                                                                 W.sub.1                                                                          W.sub.2                                                                          (wt %)                                                                            ε.sub.r                                                                  Q.sub.u                                                                          (ppm/%)                                     __________________________________________________________________________    1* 16.7                                                                             66.6                                                                             16.7                                                                             0.20  0.05                                                                             0.75                                                                             0   83.1                                                                             2260                                                                             56                                          2  "  "  "  "     "  "  0.2 82.9                                                                             2410                                                                             45                                          3  "  "  "  "     "  "  1   81.8                                                                             2170                                                                             15                                          4  "  "  "  "     "  "  3   79.5                                                                             1950                                                                             -45                                         5* "  "  "  "     "  "  10  43.1                                                                              750                                                                             -150                                        6* 22.0                                                                             60.0                                                                             18.0                                                                             0.24  0.23                                                                             0.53                                                                             0   58.8                                                                             1790                                                                             74                                          7  "  "  "  "     "  "  0.2 58.5                                                                             1920                                                                             66                                          8  "  "  "  "     "  "  1   57.8                                                                             1830                                                                             23                                          9  "  "  "  "     "  "  3   55.9                                                                             1630                                                                             -21                                         10*                                                                              "  "  "  "     "  "  10  38.5                                                                              600                                                                             -125                                        __________________________________________________________________________

                                      TABLE A1                                    __________________________________________________________________________       BaO                                                                              TiO.sub.2                                                                        RE Sm.sub.2 O.sub.3                                                                    La.sub.2 O.sub.3                                                                  Nd.sub.2 O.sub.3                                                                  Bi.sub.2 O.sub.3                                                                        τ.sub.f                               NO X  Y  Z  1-W.sub.1 --W.sub.2                                                                 W.sub.1                                                                           W.sub.2                                                                           V   ε.sub.r                                                                  Q.sub.u                                                                          (ppm/°C.)                          __________________________________________________________________________    1  15.63                                                                            66.71                                                                            15.63                                                                            0.835 0.133                                                                             0.032                                                                             2.03                                                                              77.0                                                                             2010                                                                             -86                                       2  15.63                                                                            66.71                                                                            15.63                                                                            0.624 0.122                                                                             0.254                                                                             2.03                                                                              82.2                                                                             1810                                                                             -51                                       3  15.63                                                                            66.71                                                                            15.63                                                                            0.435 0.168                                                                             0.397                                                                             2.03                                                                              85.5                                                                             1910                                                                             -35                                       4  15.63                                                                            66.71                                                                            15.63                                                                            0.281 0.196                                                                             0.423                                                                             2.03                                                                              88.1                                                                             1890                                                                             -20                                       5  15.63                                                                            66.71                                                                            15.63                                                                            0.118 0.178                                                                             0.704                                                                             2.03                                                                              91 2015                                                                             5                                         6* 14.63                                                                            68.23                                                                            14.63                                                                            0.240 0.760                                                                             0   2.51                                                                              77.5                                                                             1010                                                                             117                                       7* 14.63                                                                            68.23                                                                            14.63                                                                            0     0.644                                                                             0.356                                                                             2.51                                                                              75.4                                                                             1205                                                                             123                                       8  14.0                                                                             72.0                                                                             14.0                                                                             0.333 0.541                                                                             0.126                                                                             4.62                                                                              87.0                                                                             1750                                                                             59                                        9  14.0                                                                             72.0                                                                             14.0                                                                             0.180 0.470                                                                             0.350                                                                             4.62                                                                              91.4                                                                             1510                                                                             68                                        10*                                                                              14.0                                                                             72.0                                                                             14.0                                                                             0.440 0   0.560                                                                             4.62                                                                              73.6                                                                             1770                                                                             116                                       11*                                                                              26.5                                                                             71.5                                                                             2.0                                                                              0.340 0.280                                                                             0.380                                                                             1.05                                                                              53.1                                                                              960                                                                             110                                       12*                                                                              11.5                                                                             84.0                                                                             4.5                                                                              0.340 0.280                                                                             0.380                                                                             1.05                                                                              51.2                                                                             1060                                                                             136                                       13 21.0                                                                             72.5                                                                             6.5                                                                              0.340 0.280                                                                             0.380                                                                             1.05                                                                              54.2                                                                             1790                                                                             63                                        14 21.0                                                                             60.0                                                                             19.0                                                                             0.340 0.280                                                                             0.380                                                                             1.05                                                                              68.2                                                                             1670                                                                             51                                        15*                                                                              21.0                                                                             53.5                                                                             25.5                                                                             0.16  0.37                                                                              0.47                                                                              1.51                                                                              54.2                                                                              880                                                                             113                                       16*                                                                              8.0                                                                              60.0                                                                             32.0                                                                             0.16  0.37                                                                              0.47                                                                              1.51                                                                              53.9                                                                              940                                                                             121                                       17 11.5                                                                             76.0                                                                             12.5                                                                             0.16  0.37                                                                              0.47                                                                              1.51                                                                              71.3                                                                             1860                                                                             61                                        18 12.0                                                                             60.0                                                                             26.0                                                                             0.16  0.37                                                                              0.47                                                                              1.51                                                                              73.6                                                                             1790                                                                             33                                        19*                                                                              15.74                                                                            68.52                                                                            15.74                                                                            0.58  0.31                                                                              0.11                                                                              0   81.7                                                                             1830                                                                             55                                        20 15.71                                                                            68.40                                                                            15.71                                                                            0.58  0.31                                                                              0.11                                                                              0.10                                                                              88.6                                                                             1860                                                                             47                                        21 15.05                                                                            65.51                                                                            15.05                                                                            0.58  0.31                                                                              0.11                                                                              4.40                                                                              94.5                                                                             1960                                                                             16                                        22 14.31                                                                            66.38                                                                            14.31                                                                            0.58  0.31                                                                              0.11                                                                              5.00                                                                              85.1                                                                             1570                                                                             53                                        23*                                                                              13.12                                                                            63.76                                                                            13.12                                                                            0.58  0.31                                                                              0.11                                                                              10.00                                                                             80.9                                                                              960                                                                             115                                       __________________________________________________________________________

                                      TABLE A2                                    __________________________________________________________________________       BaO                                                                              TiO.sub.2                                                                        RE Sm.sub.2 O.sub.3                                                                    La.sub.2 O.sub.3                                                                  Nd.sub.2 O.sub.3                                                                  Bi.sub.2 O.sub.3                                                                  MnO.sub.2                                                                         ε.sub.r                                                                  Q.sub.u                                                                          τ.sub.f                           NO.                                                                              X  Y  Z  1-W.sub.1 --W.sub.2                                                                 W.sub.1                                                                           W.sub.2                                                                           V   O   -- -- (ppm/°C.)                      __________________________________________________________________________     1*                                                                              18.7                                                                             68.7                                                                             10.85                                                                            0.32  0.27                                                                              0.41                                                                              1.75                                                                              0   76.3                                                                             1790                                                                             34                                    2  18.7                                                                             68.7                                                                             10.85                                                                            0.32  0.27                                                                              0.41                                                                              1.75                                                                              0.3 77.8                                                                             2065                                                                             29                                    3  18.7                                                                             68.7                                                                             10.85                                                                            0.32  0.27                                                                              0.41                                                                              1.75                                                                              1.1 78.1                                                                             2130                                                                             23                                    4  18.7                                                                             68.7                                                                             10.85                                                                            0.32  0.27                                                                              0.41                                                                              1.75                                                                              2.0 77.6                                                                             2145                                                                             31                                     5*                                                                              18.7                                                                             68.7                                                                             10.85                                                                            0.32  0.27                                                                              0.41                                                                              1.75                                                                              3.5 75.9                                                                             1063                                                                             77                                    __________________________________________________________________________

                                      TABLE D1                                    __________________________________________________________________________       BaO                                                                              TiO.sub.2                                                                        RE Sm.sub.2 O.sub.3                                                                    La.sub.2 O.sub.3                                                                  Nd.sub.2 O.sub.3                                                                  Bi.sub.2 O.sub.3                                                                  CeO.sub.2 τ.sub.f                           No.                                                                              X  Y  Z  1-W.sub.1 --W.sub.2                                                                 W.sub.1                                                                           W.sub.2                                                                           V   (wt %)                                                                            ε.sub.r                                                                  Q.sub.u                                                                          (ppm/°C.)                      __________________________________________________________________________    1* 15.63                                                                            66.71                                                                            15.63                                                                            0.281 0.296                                                                             0.423                                                                             2.03                                                                              0   88.1                                                                             1890                                                                             28                                    2  "  "  "  "     "   "   "   0.2 89.5                                                                             1980                                                                             21                                    3  "  "  "  "     "   "   "   1   87.5                                                                             2050                                                                             8                                     4  "  "  "  "     "   "   "   3   83.2                                                                             2310                                                                             -16                                   5  "  "  "  "     "   "   "   5   75.3                                                                             1950                                                                             10                                    6* "  "  "  "     "   "   "   10  38.1                                                                             1310                                                                             65                                    7* 14.31                                                                            66.38                                                                            14.31                                                                            0.58  0.31                                                                              0.11                                                                              5.0 0   85.1                                                                             1570                                                                             53                                    8  "  "  "  "     "   "   "   0.2 86.3                                                                             1630                                                                             47                                    9  "  "  "  "     "   "   "   1   88.6                                                                             1890                                                                             26                                    10 "  "  "  "     "   "   "   3   84.7                                                                             2140                                                                             12                                    11 "  "  "  "     "   "   "   5   78.3                                                                             1710                                                                             29                                    12*                                                                              "  "  "  "     "   "   "   10  42.6                                                                             1290                                                                             92                                    __________________________________________________________________________

                                      TABLE D2                                    __________________________________________________________________________       BaO                                                                              TiO.sub.2                                                                        RE Sm.sub.2 O.sub.3                                                                    La.sub.2 O.sub.3                                                                  Nd.sub.2 O.sub.3                                                                  Bi.sub.2 O.sub.3                                                                  PbO       τ.sub.f                           No.                                                                              X  Y  Z  1-W.sub.1 --W.sub.2                                                                 W.sub.1                                                                           W.sub.2                                                                           V   (wt %)                                                                            ε.sub.r                                                                  Q.sub.u                                                                          (ppm/°C.)                      __________________________________________________________________________    1* 15.63                                                                            66.71                                                                            15.63                                                                            0.281 0.296                                                                             0.423                                                                             2.03                                                                              0   88.1                                                                             1890                                                                             28                                    2  "  "  "  "     "   "   "   0.2 88.7                                                                             1840                                                                             21                                    3  "  "  "  "     "   "   "   1   89.9                                                                             1780                                                                             13                                    4  "  "  "  "     "   "   "   3   93.5                                                                             1670                                                                             5                                     5  "  "  "  "     "   "   "   5   95.2                                                                             1530                                                                             20                                    6* "  "  "  "     "   "   "   10  82.6                                                                              820                                                                             86                                    7* 14.31                                                                            66.38                                                                            14.31                                                                            0.58  0.31                                                                              0.11                                                                              5.0 0   85.1                                                                             1570                                                                             53                                    8  "  "  "  "     "   "   "   0.2 86.0                                                                             1540                                                                             46                                    9  "  "  "  "     "   "   "   1   87.2                                                                             1490                                                                             34                                    10 "  "  "  "     "   "   "   3   89.7                                                                             1440                                                                             26                                    11 "  "  "  "     "   "   "   5   92.5                                                                             1380                                                                             41                                    12*                                                                              "  "  "  "     "   "   "   10  81.3                                                                              720                                                                             103                                   __________________________________________________________________________

                                      TABLE D3                                    __________________________________________________________________________       BaO                                                                              TiO.sub.2                                                                        RE Sm.sub.2 O.sub.3                                                                    La.sub.2 O.sub.3                                                                  Nd.sub.2 O.sub.3                                                                  Bi.sub.2 O.sub.3                                                                  Al.sub.2 O.sub.3                                                                        τ.sub.f                           No.                                                                              X  Y  Z  1-W.sub.1 --W.sub.2                                                                 W.sub.1                                                                           W.sub.2                                                                           V   (wt %)                                                                            ε.sub.r                                                                  Q.sub.u                                                                          (ppm/°C.)                      __________________________________________________________________________    1* 15.63                                                                            66.71                                                                            15.63                                                                            0.281 0.296                                                                             0.423                                                                             2.03                                                                              0   88.1                                                                             1890                                                                             28                                    2  "  "  "  "     "   "   "   0.1 87.8                                                                             1980                                                                             17                                    3  "  "  "  "     "   "   "   0.5 86.2                                                                             2120                                                                             6                                     4  "  "  "  "     "   "   "   1   84.6                                                                             1980                                                                             -13                                   5  "  "  "  "     "   "   "   3   78.6                                                                             1780                                                                             -39                                   6* "  "  "  "     "   "   "   10  46.5                                                                              920                                                                             -118                                  7* 14.31                                                                            66.38                                                                            14.31                                                                            0.58  0.31                                                                              0.11                                                                              5.0 0   85.1                                                                             1570                                                                             53                                    8  "  "  "  "     "   "   "   0.1 84.9                                                                             1690                                                                             39                                    9  "  "  "  "     "   "   "   0.5 83.6                                                                             1830                                                                             23                                    10 "  "  "  "     "   "   "   1   82.2                                                                             1660                                                                             -8                                    11 "  "  "  "     "   "   "   3   76.7                                                                             1510                                                                             -28                                   12*                                                                              "  "  "  "     "   "   "   10  39.8                                                                              710                                                                             -89                                   __________________________________________________________________________

What is claimed is:
 1. A dielectric ceramic for microwave applicationsconsisting essentially of the components barium oxide (BaO), titaniumdioxide (TiO₂), samarium oxide (Sm₂ O₃), lanthanum oxide (La₂ O₃) andneodymium oxide (Nd₂ O₃) represented by the formula:

    x BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }

where X, Y, Z lie in the ranges:

    11.0≦X≦22.0

    60.0≦Y≦75.0

    6.0≦Z≦28.0

    X+Y+Z=100

expressed in mole %, and

    0≦W.sub.1 ≦0.35

    0<W.sub.2 <1

    0<(1-W.sub.1 -W.sub.2)<1

where W₁, W₂ and (1-W₁ -W₂) are mole ratios and wherein said componentsare present in sufficient amounts as to produce a dielectric ceramichaving a high dielectric constant, a high unloaded Q and a temperaturecoefficient variable above and below Oppm/°C.
 2. A dielectric ceramicaccording to claim 1 in which, MnO₂ is also added, as a supplementaryconstituent, to the extent of no more than 3 wt %.
 3. A dielectricceramic according to claim 1 in which, Al₂ O₃ has also been added, as asupplementary constituent, to the extent of no more than 3 wt %, thiscorresponding to 0.0563 mole per mole of the main constituents.
 4. Adielectric ceramic for microwave applications consisting essentially ofthe components barium oxide (BaO), titanium dioxide (TiO₂), samariumoxide (Sm₂ O₃), lanthanum oxide (La₂ O₃), neodymium oxide (Nd₂ O₃) andbismuth oxide (Bi₂ O₃), represented by the formula:

    X BaO.Y TiO.sub.2.Z {(Sm.sub.2 O.sub.3).sub.1-W1-W2 (La.sub.2 O.sub.3).sub.W1 (Nd.sub.2 O.sub.3).sub.W2 }.V Bi.sub.2 O.sub.3

where X, Y, Z and V lie in the ranges:

    11.5≦X≦21.0

    60.0≦Y≦76.0

    6.5≦Z≦26.0

    0.1≦V≦5.0

    X+Y+Z+V=100

expressed in mole %, and

    0<W.sub.1 <1

    0<W.sub.2 <1

    0<(1-W.sub.1 -W.sub.2)<1,

where W₁, W₂ and (1-W₁ -W₂) are mole ratios and wherein said componentsare present in sufficient amounts as to produce a dielectric ceramichaving a high dielectric constant, a high unloaded Q and a temperaturecoefficient variable above and below 0° C.
 5. A dielectric ceramicaccording to claim 4 in which, to MnO₂ is also added to the extent of nomore than 2 wt %.
 6. A dielectric ceramic according to claim 4, in whichcerium oxide (CeO₂) is also added, as a supplementary constituent, tothe extent of no more than 5 wt %, this amount corresponding to 0.0606mole per mole of the main constituents.
 7. A dielectric ceramicaccording to claim 4 in which, to lead oxide (PbO) is also added, as asupplementary constituent, to the extent of no more than 5 wt %, thiscorresponding to 0.0463 mole per mole of the main constituents.
 8. Adielectric ceramic according to claim 4, in which aluminum oxide (Al₂O₃) is also added, as a supplementary constituent, to the extent of nomore than 3 wt %, this corresponding to 0.0609 mole per mole of the mainconstituents.
 9. A dielectric ceramic according to claim 1 in which thetemperature coefficient is in the low temperature coefficient range. 10.A dielectric ceramic according to claim 4 in which the temperaturecoefficient is in the low temperature coefficient range.
 11. Adielectric ceramic according to claim 1 in which the temperaturecoefficient is in the vicinity of Oppm/°C.
 12. A dielectric ceramicaccording to claim 4 in which the temperature coefficient is in thevicinity of Oppm/°C.
 13. A dielectric ceramic according to claim 9 inwhich the temperature coefficient is below Oppm/°C.
 14. A dielectricceramic according to claim 10 in which the temperature coefficient isbelow Oppm/°C.